Electrohydrodynamic apparatus and method



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ELECTROHYDRODYNAMIC APPARATUS AND METHOD Filed June 20, 1967 3 Sheets-Sheet 1 JAMES R MELCHER llVVE/VTOP ATTOR/VY Aug. 26, 1969 J. R. MELCHER ELECTROHYDRODYNAMIC APPARATUS AND METHOD 3 Sheets-Sheet 2 Filed June 20, 1967 a l-V FIG.2

HHHUJII llll IHIHIIHUUUHHHHllllllll HII HHIHIHIHHHHHHIHHL .T u IT ATTOR) Aug. 26, 1969 J. R. MELCHER ELECTROHYDRODYNAMIC APPARATUS AND METHOD Filed June 20, 1967 3 Sheets-Sheet 5 SECTION 5-5 FIG.

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JAMES R. MELCHER ATTOREY United States Patent 3,463,944 ELECTROHYDRODYNAMIC APPARATUS AND METHOD James R. Melcher, Lexington, Mass, assignor to Massachusetts Institute of Technology, Cambridge, Mass, a

corporation of Massachusetts Filed June 20, 1967, Ser. No. 647,526 Int. Cl. H02k 45/00,- G211! 7/02 US. Cl. 310-40 20 Claims ABSTRACT OF THE DISCLOSURE The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42 U.S.C. 2457).

Apparatus for pumping liquids and gases have been provided wherein, for example, the fluid is placed in an ionized state and thereafter acted upon by an imposed electric potential, as in the case of ion-drag devices, or acted upon by a magnetic field, as in the case of magnetohydrodynamic devices. In both instances, as mentioned, the fluid is ionized and in the case of the ion-drag device the electrodes are actually in electrical contact with the fluid. By appropriate changes in the apparatus the fluid can be made to perform work and transfer energy to the electric or the magnetic field and in this way change the apparatus to a generator. The foregoing is discussed briefly in an article entitled Traveling-Wave Induced Electroconvection, by the present inventor, published in The Physics of Fluids, vol. 9, No. 8, pages 1548 et. seq., August 1966. In the article reference is made, also, to apparatus of the type herein disclosed wherein an induction pumping and generating are performed by the use of an electric potential wave traveling in a direction perpendicular to a resistance gradient in the fluid or other material acted upon. Whereas the prior art devices described above function as a result of interaction between a field and a highly conductive medium, as is the case of the magnetohydrodynamic device, or between a field and an ionized medium, the apparatus and method of the present invention contemplate, and it is an object of the invention to provide, apparatus and method to effect reaction between an electric potential field and a high resistance medium without the need for ionization of the medium by some external means and without the need for electrical contact with the medium.

Another object is to provide apparatus which may be used either as a pump or as a generator, but wherein interaction to effect either function is accomplished without the necessity for electric connection between the driving means and the driven means.

Still another object to provide apparatus wherein the energy transfer is an electrohydrodynamic one.

' A further object is to provide apparatus in which the transfer is between an electro-quasistatic field and the high resistance material.

These and other objects will become evident in the description to follow and will be particularly pointed out in the appended claims.

Broadly, and by way of summary, the invention relates to apparatus adapted to effect interaction between an electroquasistatic field and a high resistance material having a transverse electric conductivity gradient. Mean is provided for introducing to the material an electro-quasistatic field having effective transverse and longitudinal components, and further means is provided for introducing relative movement between the field and the material in a direction orthogonal to the transverse component, the angular frequency of the field relative to the material being established and maintained at a value substantially equal to the inverse of the electric relaxation time constant of the material.

The invention will now be described in connection with the appended drawings, in which,

FIG. 1 is a perspective view, partly schematic in form and partially cut away, of one form of apparatus adapted to effect movement of a high resistance material by interaction of the material and a traveling wave electroquasistatic field;

FIG. 2 shows, graphically, the interaction between the material and the wave at one particular instant of time;

FlG. 3 is a graphic representation similar to FIG. 2 to show equi-potential lines in the material at the particular instant of time depicted in FIG. 2;

FIG. 4 is a partial view taken upon the line 44 in FIG. 1 looking in the direction of the arrows; and

FIG. 5 is a partial view taken upon the line 5-5 in FIG. 4 looking in the direction of arrows.

Before going into a detailed discussion of the invention, it is in order to discuss the theory upon which the present invention is based, first, in connection with the electrohydrodynamic pum function.

An electro-quasistatic traveling wave potential may be established to travel, for example, in some direction X, in a manner to be hereinafter discussed, at some angular frequency, w. A high resistanec material (liquid, gas or solid), displaced at some distance from the source of the traveling wave with air occupying the space there-between, is subject to the influence of the electric field of the wave, which passes transversely (in the Z direction) through the air space and into the material, the greatest effect occurring at the interface between the material and the air because of the large transverse electric resistance gradient that occurs there. The electric field will at some point along the interface induce changes in the material, of opposite polarity to the electric charges of the traveling wave opposite that point, to relax toward that point. In the absence of relative movement in the X direction between the material and the wave, the only force therebetween would be in the transverse or Z direction. However, movement of the wave in the X direction, if effected at an angular frequency (to) relative to the material of a value substantially equal to the inverse of the electric relaxation time constant of the material, will result in a lagging of the induced charges behind the charges of the wave, thereby to effect a force in the X direction upon the material at the interface.

It has been found, moreover, that, though the transverse conductivity gradient may be provided by having two mediums of dissimilar conductivities disposed in the contiguous fashion described above, the gradient may also be provided by effecting temperature differentials between regions of the material in the transverse direction, as well. (See an article entitled Traveling-Wave Bulk Electroconvection Induced Across a Temperature Gradient, Melcher et al., The Physics of Fluids, June 1967.) The means whereby the transverse resistance gradient is provided is not important, merely that a gradient exists. Furthermore, whereas one transverse conductivity gradient may produce material movement in the X direction, a negative of this gradient in the same circumstance will produce movement in the minus X direction.

In the foregoing explanation, it is the electric wave energy which is made to move in space thereby to effect movement of the high resistance material, the energy for such movement being extracted from the electric wave. The invention, however, may be made to perform a generator function. In this second function, energy is removed from the material which is driven at some velocity faster than that of the electro-quasistatic wave. Again the relative movement between the material and the angular frequency of the wave is substantially equal to the inverse of the electric relaxation time constant of the material.

Turning now to the drawings, a high resistance material is shown at 1 in FIG. 1 held within an annular container 2. To simplify explanation herein, the bottom of the container 2 is shown disposed in the plane designated XY and the depth thereof is shown to be in the Z direction, the magnitude being designated a. A plurality of adjacent electrodes 3 are located in an XY plane some distance d above the material 1 in a circular configuration; air, designated by the numeral 11 in FIG. 5, occupies the space between the said material and the lowermost surface of the electrodes.

An electro-quasistatic potential wave as, for example, the wave shown graphically at 20 in FIGS. 2 and 3, establishes an electro-quasistatic field represented by the equipotential lines 21 and 22, etc., representing a positive transverse field at two equipotential values in the material, and 21 and 22' etc., representing a negative transverse field again at two equipotential values in the material, in FIG. 3. Assume that at any particular instant of time the conditions represented in FIG. 2 exist. The electric potential represented by the wave 2% introduces an electric charge, which may be represented by the negative traveling-wave charges shown at 23, thereby establishing an electro-quasistatic field having effective transverse and longitudinal components, as previously discussed. The electroquasistatic field induces charges, which may be represented by the positive surface charges shown at 24, to relax toward the interface 4 between the material 1 and the air layer 11. Assuming that the wave 20 is made to travel in the X direction, the surface charges 24 will lag behind the traveling wave charges 23, as shown. As the wave 20 moves along in the X direction, a shear force will be exerted by the wave upon the material, at the interface 4, having a component also in the X direction, and the material will tend to move in the direction of wave movement. Further, if relative movement between the material and the wave 20 in the X or orthogonal direction is maintained at a rate or value such that the angular frequency relative to the moving material is substantially equal to the inverse of the electric relaxation time (where the electric relaxation time equals permittivity/electrical conductivity) of the material 1, the surface charges 24 will continue to lag the traveling wave charges by some fixed amount. The movement in the X direction of the material at the interface will, by viscous shear, effect movement of the remainder thereof.

The traveling wave, as that shown graphically at 20 in FIGS. 2 and 3, and designated by the arrow A in FIG. 4, may be imposed by passing electric potential from a D-C source 10 through brushes 11 and 11' to slip rings 6 and 7, respectively, thence to further brushes 12 and 13, respectively, to a plurality of commutators, represented schematically in FIG. 1 by a plurality of regions 3. The commutators 3' are connected by a plurality of conductors to the individual electrodes 3, shunt resistances 8 between said electrodes being provided to cause the applied potential to approach the sinusoidal wave shape shown at 20. The further brushes 12 and 13 are secured to the far ends of an arm 40 secured to a central shaft 39 driven by a variable-speed electric motor 36 which is adapted to rotate the center shaft at some angular frequency r. (n=w in the apparatus shown). Although not required for general usage the velocity of the material 1 may be measured by a transducer 50, which may be a pitot tube or other velocity-measuring device, the value from the transducer 50 being fed to a suitable readout device as which, in turn, feeds a signal to a suitable control 51 to control the speed of the drive motor 36 and a variable impedance device 38 to control voltage, as required. In this fashion, the angular frequency w of the traveling wave field may be maintained at a value relative to the material that is the inverse of the electric relaxation time constant of said material, the angular velocity being adjustable to maximize movement of the material. However, the force vs. frequency curve for many materials of interest is not highly sensitive to frequency so that for any particular material 1 an acceptable range of frequencies of operation can be predetermined so that the angular frequency a: can be established and maintained at the predetermined value.

In the apparatus shown in FIG. 1 the electrodes 3 are shown adjacently disposed in a circular configuration, being located and secured within a plastic layer 3". The circularly disposed electrodes 3 of FIG. 1 are shown in the schematic representation of FIGS. 2 and 3 disposed along a straight line and the number of electrodes is increased. In a straight line arrangement of electrodes 3, an electro-quasistatic traveling wave, as shown at 20, may be created by connecting a source of A-C potential through phase shifter means to successive electrodes 3.

As previously mentioned, the transverse conductivity gradient may be created by having a high resistance material 1 with an air layer 11 between the material and the electrodes; but a temperature differential may also be used to create the gradient since the conductivity of slightly conducting materials often depends strongly on temperature. Referring to FIG. 5, the material may be a liquid which fills the cavity shown to contain the material 1 and air 11, in which case the interface 4 would not exist. The temperature differential may be created by having a quantity of ice water 40* (in a container 41) in thermal contact with the lowermost part of the liquid through a bottom surface 33 of good thermal conductivity material and a quantity of hot oil 14 in thermal contact with the uppermost surface of the liquid 1. The electrodes may make mechanical contact with the liquid 1, but electrical contact is not necessary and, indeed, does not exist in the illustrated device when a thin plastic material 3" separates the two and, in addition, isolates the oil 14 from the high resistance liquid 1.

The side walls of the annular container 2, shown at 30 and 31, are made of a transparent plastic material to enable observation of the material 1 therein, but other insulators may also be used. The bottom 33 may be made of metal or some other conductive means, but an insulator would serve as well. In the event that it is desired to use the apparatus as a generator, the necessary flow of the liquid 1 may be effected by an electric-motor-driven pump 17 or other suitable device.

The invention herein disclosed is useful to move a fluid or other material 1 which has been described as having high resistance. In this respect it should be noted, however, that if the resistance is too high, few or no changes will relax to the interface; conversely, if the resistance is too low, charges will relax instantaneously from one point to the other on the interfaces as the traveling wave moves along, and no shear, and thus no fluid movement, will occur. Either the pumping function or the generator function can take place only if there is slip between the electro-quasistatic traveling wave and the fluid, that is, when the phase velocity (angular frequency/wave number) of the wave is greater or less than the fluid velocity. Furthermore, the bulk charge of the fluid is zero (even though conduction currents exist within the volume of the fluid); and the net charge at the interface is also zero. Reference has been made herein to electro-quasistatic fields which may appear as traveling waves. The term electro-quasistatic denotes a wave that performs the described functions by virtue of the electrostatic properties of the field; although the field may by changing in time and space. The reaction between the field and the material ditfers from magnetohydrodynamic devices in which the material is a highly conductive fluid and the magnetic properties of the field are relied upon to accomplish the desired result, and ion-drag devices in which an electric field, introduced through electrodes immersed in the fluid, react with ions introduced into the fluid at some point remote from the electrodes.

The invention has been disclosed in connection with a horizontally oriented device, but other orientations may be used as well, as long as the further limitations are met. For example, the concept disclosed may be used to effect vertical movement of insulating oil within the coil area of electric power transformers, and for such application the electrodes 3 would be vertically oriented.

Also, the electrical energizing source can be replaced by twoor three-phase generators by superimposing outof-phase standing waves on electrodes of varying widths. Or, for example, a six-phase source of power can be used to energize adjacent uniform-sized electrodes and this would approach a sinusoidal wave-shape for the traveling wave.

These and other modifications of the invention will occur to those skilled in the art and all such modifications are considered to be within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A method of effecting interaction between an electroquasistatic field and a high resistance material having a transverse electrical conductivity gradient, that comprises, introducing to the material an electro-quasistatic field having effective transverse and longitudinal components, eifecting relative movement between said field and the material in a direction orthogonal to the transverse component, and maintaining the angular frequency of the field relative to the material at a value substatially equal to the inverse of the electri relaxation time constant of the material.

2. A method as claimed in claim 1 and in which the material comprises a high resistance liquid separated from the source of the electro-quasistatic field by a layer of gas, the said field gradient being at the interface of the liquid and the gas, said relative movement being efiected along a path parallel to said interface.

3. A method as claimed in claim 2 and in which the relative movement is eifected by establishing an electroquasistatic traveling wave, the phase velocity of which in the said orthogonal direction is greater than the velocity of the material in said direction.

4. A method as claimed in claim 3 and in which induced Charges of opposite polarity to the charges of the electro-quasistatic traveling wave relax through the liquid to form a wave of surface charges at the interface, said angular frequency being maintained at a rate whereby the induced charges lag the electro-quasistatic traveling wave charges.

5. A method as claimed in claim 2. and in which the traveling wave comprises a plurality of regions of periodically increasing and decreasing electric potentials.

6. A method as claimed in claim 1 and in which the electro-quasistatic field is created by a traveling wave propagated in a direction orthogonal to said transverse component and the conductivity gradient is adjusted to effect movement of the material in a direction opposite to that of the traveling wave as a result of said interaction.

7. A method as claimed in claim 3 and in which the rate of relative movement between the electro-quasistatic field and the material is adjusted to maximize the velocity of the material in the said direction.

8. A method as claimed in claim 1 and in which the relative movement is effected by establishing an electro-quasistatic traveling wave to propagate in the said direction and driving the material in the said direction at a velocity greater than the velocity of the traveling wave, thereby to effect energy transfer from the material to the wave.

9. A method as claimed in claim 1 and in which the material is a composite comprising two materials having dissimilar conductivities and the said conductivity gradient occurs at the interface between the said two materials.

16. A method as claimed in claim 1 and in which a transverse temperature diiferential is established in the material, thereby to create the transverse conductivity gradient.

11. A method as claimed in claim 1 and in which the conductivity gradient is created by inhomogeneity of the material.

12. Apparatus for effecting interaction between an electro-quasistatic field and a high resistance material having a transverse conductivity gradient, that comprises, means for introducing to the material an electro-quasistatic field having effective transverse and longitudinal components, means for introducing relative movement between said field and the material in a direction orthogonal to the transverse component, the angular frequency of the field relative to the material being maintained at a value substantially equal to the inverse of the electric relaxation time constant of the material.

13. Apparatus as claimed in claim 12 and in which the field introducing means comprises, a plurality of electrodes adjacently disposed along the said orthogonal direction and a source of time varying electric potential connected thereto.

14. Apparatus as claimed in claim 13 and in which the material is a composite comprising two mediums having dissimilar conductivities, the said conductivity gradient occurring at the interface between the two mediums.

15. Apparatus as claimed in claim 14 and in which the plurality of electrodes lie in a plane substantially parallel to the said interface.

16. Apparatus as claimed in claim 13 and in which the source of electric potential is adapted to connect sequentially to adjacent electrodes along the said orthogonal direction thereby to provide an electro-quasistatic traveling wave moving in said orthogonal direction.

17. Apparatus as claimed in claim 13 and in which the source of electric potential is adapted to introduce diiferent values of electric potential to adjacent electrodes thereby to create regions alternately of positive and negative electric potential along the said orthogonal direction, the electric potential at the said regions varying in time from positive potential values to negative potential values along the said direction.

18. Apparatus as claimed in claim 13 and in which the source of electric potential comprises a D-C power supply connected to brushes in electric contact with said electrodes, the brushes being moved in said direction to effect sequential connection to adjacent electrodes.

19. Apparatus as claimed in claim 18 in which the electrodes are positioned to form a circular track and the brushes are disposed diametrically from one another on the circle, movement thereof being effected by rotation about the center of the circle.

20. Apparatus as claimed in claim 12 and in which means is provided to establish a transverse temperature differential in the material thereby to create a transverse electrical conductivity gradient therein.

References Cited UNITED STATES PATENTS 3,264,998 8/1966 Dingman .1031

DAVID X. SLINEY, Primary Examiner US. Cl. X.R. 103-4; 3105 

